Days Between Two Dates

This formula finds the gap between two calendar dates by converting each date into a Julian Day Number (JDN), which counts days on a continuous scale. Once both dates are on the same day-count timeline, subtracting the earlier JDN from the later one gives the exact number of whole days between them, with leap days automatically included if they occurred in the interval. The result is a signed difference: positive if the second date is later, negative if it is earlier.

Use this when you need an exact day count between dates in scheduling, billing, project timelines, loan periods, or age calculations. It is especially useful in science and programming because it avoids errors from differing month lengths and leap years.

• Subtracting calendar dates directly without converting to a continuous day count
• Forgetting that leap days can change the result in spans that include February 29
• Mixing up the order of subtraction and getting the sign reversed